Tree Decay Detection

Consultancy-(2)We employ a team of dedicated and experienced surveyors all qualified to the Lantra Professional Tree inspection level. However, we understand that at times more information on the condition of a tree is needed before any management regime can be agreed. In order to enable us to provide such advice to our clients, our consultants have extensive experience in carrying more detailed investigations into the condition of important trees.

To enable them to carry out this work they will use Resistographs, Sonic Tomographs (Picus) and core sample analysis.


Decay investigation and mapping using an IML- RESI F-Series. The IML Resistograph is used to establish the strength of wood, without the need for destructive testing. It consists of a hand-portable, electrically-powered drill, the auger end of which is ‘spade-bit’ shaped and extremely narrow.


As the subject tree is drilled sound wood being denser than decayed wood offers greater resistance to the drill bit as it passes through the wood. This resistance is recorded electronically across the radius of the section being tested. The depth of drilling is dependent on the drill length and dimension of the tree part being tested.

The measurement depth is recorded in centimetres while the amplitude (resistance) reading is given as a percentage across a range of 0 to 100%. The readings allow the Arboriculturalist to assess the internal condition of the subject tree. As with all diagnostic tools, considerable experience in use and interpretation of data is required to ensure that an accurate conclusion and or recommendation is made.


This method of decay detection is based on the fact that solid wood is a better sound wave conductor than wood that is decayed or structurally damaged.

The Picus Sonic Tomograph consists of a set of sensors which are strategically placed around the area of the tree previously identified as potentially having decay or a structural fault. Each sensor is connected to a nail which is tapped through the bark into contact with the wood. This process is virtually non-invasive to the tree’s system. The sensors are connected by data cable to a power supply and laptop computer.

Each nail is tapped in turn and the sound wave flight paths are measured by each of the sensors. This results in a dense network of sound velocities through a cross section of the tree.

The velocity of sound through wood depends on the degree of elasticity and density of the material. Tree damage such as white rot, brown rot, soft rot, cavities and cracks reduce the elasticity and density of the wood.

The data from the sensors is translated by the computer software into a full colour tomogram of the cross section of the tree. This tomogram gives information about the presence of decay, cavities and faults in the tree. Features such as remaining wall thickness, opening angle of cavities and percentage of solid, decayed or altered wood can be measured by the computer. Final analysis of the tomogram should be undertaken by an experienced Arboricultural Consultant and related to the trees condition, structure and position